I am an engineer-turned-school-maths teacher....
I love to see the sparkles of understanding in the eyes of my students.... It is really exciting to see I was part of this enlightenment process.... I find myself both inspired and inspiring!
I love doing math with children & sharing my love of math and children with parents and teachers... Check the websites www.about.me/rupesh.gesota and www.supportmentor.weebly.com to know more about me & my math-adventures...

Tuesday, July 5, 2016

"No, this number will give us no. of months, not years ! "

The other day we were working on some problem, where we felt the need to figure out the date after some fixed amount of days from a given date.

So basically, the problem was -

Whats the date after 3166 days from 30th June 2016 ?

The immediate response that came from them --

"Lets divide 3166 by 12 to get the number of years we need to go ahead."

I could see a problem ahead, however for some reason I chose to stay mum and go with the flow (chorus).

Could you figure out the problem? :-) and why would have students committed this mistake?

We did the division.

"Ok... So what have we got? What does this 263 represent?"

This time (and I am glad) that the size of chorus was much smaller. In fact, when some of them shouted "263 years" there were others to counter them --

"Ah, how can its be 263 YEARS? Isn't it too big, for 3166 days?"

I was now expecting a correction. But can you guess what happened?

"Sir, It's not 263 YEARS, it is 263 MONTHS! "

Gosh !! And I was again pulled back. But then, I had still something to pick upon...

"Ok... So you feel 3166 days = 263 MONTHS?"

"Yes....", but this time it was a little less louder...perhaps my interrogation had shook their confidence a bit :)

"Ok... Can you verify this using other method?"

Silence....

So, I had to intervene after some time.

"Ok... Lets say we have 400 days... what if we need to estimate the number of months? I don't want the exact figure."

One of them was quick to catch this --

"Sir, it is about 13-14 months."

"What say class? Do you all agree with this?" I waited till the green (or red) signal. But soon all agreed, and I continued.

"Ok... So we have estimated that 400 days is around 13-14 months. What do we do calculate now?"

"Lets divide by 12."

"Ok, so you mean the way we did for 3166 days?"

"Yes!"

"So? ..... 400 days = 33 months, right?"

This shocked them !! To make it worse, my taunting smile salted their wound :)

I chose to hold on for a while. I was sure one of them will come up with the problem or solution. The growing duration of silence started disappointing me a bit, and I was about to intervene, when..........

"Sir.. I got 13 when I divided 400 by 30"

And all heads turned to this last bench girl...

"So what does it mean, Vaishnavi?"

"We divided by the wrong number... It should not be 12, it should be 30."

I wrote this on the board and gave the class some time to comprehend this fact. And in no time, they got the point.

But how can I leave them so easily? They were asked to reason as to what made them do the mistake... and why one should divide by 30 and not 12... And they explained this quite satisfactorily.